Is there a way to transmit all calendars, tasks, and contacts of my users (only two) to a new installation? It is important for us that all old appointments are also preserved. We are talking about 8 years.
You could simply export the calendars as
.ics files and your contacts as
.vcf files (in the bottom left of the corresponding apps in the Settings section).
You can import those files on your new instance the same way.